1. Field of the Invention
It is a principal object of the present invention to provide a variable rate rectangular matched filter. More particularly, it is an object of the present invention to provide a filter with a sampled output that closely represents the intregal of the input between samples and is operable in a circuit environment in place of a perfect matched filter.
2. Description of the Prior Art
Heretofore several different types of circuits were employed for increasing the signal to noise ratio of periodically keyed data. Such circuits are commonly recognized as being substitutes for perfect rectangular matched filters. A typical example of such circuit is known as an integrate and dump circuit which requires alternating storage and discharge buffers in order to provide continuous output indicative of a data stream. Such integrate and dump circuits are recognized to be basically analog devices and are designed to accommodate a fixed data rate.
Another form of substitute for a perfect matched filter is known as a lumped element filter which employs resistors, capacitors and inductive reactance elements to provide a rather complex analog arrangement which has the same shortcomings as the integrate and dump circuit but may be implemented in the form of a single filter. The lumped element filter is recognized as not being as accurate an estimate as the integrate and dump circuit is to a perfect rectangular matched filter and also is basically an analog device whose frequency is fixed according to the filter design.
Another form of substitute for a perfect matched filter is a tap delay line which is basically a fixed rate analog device which operates on the basic principle of accumulating a plurality of delayed outputs from a tap delay line. The summation of the delayed outputs provides the matched filtered substitute output.
There is an unmet requirement for a simple circuit structure which operates over a broad range of frequencies to provide a variable rate near perfect rectangular matched filter output.